WO2006064799A1

WO2006064799A1 - Composite metal oxide photocatalyst exhibiting responsibility to visible light

Info

Publication number: WO2006064799A1
Application number: PCT/JP2005/022870
Authority: WO
Inventors: Yoshihiro Nakato; Haimei Liu; Ryuhei Nakamura
Original assignee: Osaka University; The New Industry Research Organization
Priority date: 2004-12-13
Filing date: 2005-12-13
Publication date: 2006-06-22
Also published as: US20080105535A1; JPWO2006064799A1

Abstract

A photocatalyst comprising a composite metal oxide which is prepared by combining two photocatalyst systems of TiO2 and BiVO4 and contains elements of Bi, Ti and V as component elements. The above photocatalyst is novel, and exhibits high responsibility to visible lights, a great quantum efficiency, and a photocatalyst activity superior to that of a conventional photocatalyst. Especially, BiTiVO6, which is obtained in the case of the compounding ratio of 1 : 1, can be a photocatalyst exhibiting markedly high activity under visible lights. Further, a composite metal oxide represented by a general formula: BiTiMO6, wherein M represents at least one element selected from the group consisting of V, Nb and Ta, can be a photocatalyst exhibiting high activity under visible lights.

Description

Specification

Composite metal oxide photocatalyst with visible light response

Technical field

[0001] The present technology relates to a photocatalyst comprising a novel compound having visible light responsiveness, and in particular, photocatalyst for water splitting capable of efficiently generating photocurrent by photooxidizing water (generating oxygen). The present invention relates to a photocatalyst capable of efficiently decomposing an organic substance such as a medium or methanol under visible light.

Background art

[0002] In recent years, photocatalysts using metal oxides such as TiO have been actively studied and technically developed.

2

. In addition, as an application example of photocatalysts such as TiO, water can be photodecomposed using photocatalysts.

2

A method for producing hydrogen is known.

[0003] However, all photocatalysts such as TiO have a large band gap of 3 eV or more.

2

Therefore, since it responds only to ultraviolet light with a wavelength of 400 nm or less, which is contained in a small amount of sunlight, there is a problem that the efficiency is low in general use on the ground. Another problem is that holes and electrons generated by absorbing light having a wavelength longer than the energy of the band gap have opposite charges, so recombination is likely to occur and photocatalytic activity does not continue. .

[0004] Recently, visible light-responsive photocatalysts have been actively researched and some reports have been made to overcome these problems. For example, bismuth vanadate (BiVO) fine powder

4 It has been reported to improve the visible light response by improving the manufacturing method (Patent Document 1, Patent Document 2). In addition, nitrogen, carbon, sulfur, and transition elements such as chromium are added to TiO.

2

Research has been conducted to increase the sensitivity of visible light response.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-24936

Patent Document 2: Japanese Patent Laid-Open No. 2001-2419

Disclosure of the invention

Problems to be solved by the invention

[0006] The present invention is that the activity of the visible light responsive photocatalyst in the background art is not sufficient. The purpose of this is a highly active photocatalyst that can exhibit its photocatalytic function efficiently even with sunlight, and its photocatalytic activity disappears even if it is in the form of a fine particle film or suspended in water. It is an object of the present invention to provide a photocatalyst that can be suitably used for photolysis of water, for example, water. Titanium dioxide (Ti〇) is a known photocatalyst vanadate

2

Compared to bismuth (BiV〇), a highly active photocatalyst that is responsive to visible light

Four

By using visible light such as sunlight and fluorescent lamps, the purpose is to broaden the application field for applications such as antifouling, deodorizing and antibacterial purposes indoors and in cars.

Means for solving the problem

[0007] As a result of diligent research on a highly efficient solar water splitting system based on interface nano-control, the present inventors have shown that the composite metal oxide represented by the composition formula BiTiVO has a high response to visible light.

6

And succeeded in producing a highly active photocatalyst that enables water decomposition by sunlight.

[0008] The first aspect of the present invention is to combine two photocatalytic systems of TiO and BiVO,

twenty four

As mentioned above, composite metal oxides containing elements of Bi, Ti, and V can be photocatalysts with high activity under visible light. Here, two photocatalytic systems of TiO and BiVO have a molar ratio of 1: 9 to 9:

twenty four

A composite metal oxide containing Bi, Ti, and V elements as composition elements can be a photocatalyst having high activity under visible light. In particular, BiTiVO obtained with a blending ratio of 1: 1 is preferable as a photocatalyst having remarkably high activity under visible light. In other words, Ti〇 and Bi

6 2

The mixing ratio of the two photocatalytic systems of VO is a force that can be freely changed. A molar ratio of 1: 1 is high.

Four

It is preferable as a photocatalyst having a property.

Two photocatalytic systems of TiO and BiVO can be mixed in a molar ratio of 1: 9 to 9: 1.

twenty four

The reason why composite metal oxides containing Bi, Ti, and V elements as compositional elements can be photocatalysts having high activity under visible light is as follows: BiVO shown in FIG. 18 and BiTiVO of the present invention

4 6

The XRD pattern diagram and the XRD pattern diagram of TiO and BiTiVO of the present invention are almost the same.

2 6

This is because it can be considered that the structure has replaced Ti4 + (0.605A) and V5 + (0.59A). For this reason, Ti〇 and Bi

2

Even if two photocatalysts of VO are blended in a fairly free ratio, it can be a photocatalyst

Four

available. However, BiTiVO obtained at a mixing ratio of 1: 1 has the highest activity under visible light. It is considered as a photocatalyst. FTO is fluorine-doped tin oxide.

From the examples to be described later, the two photocatalytic system forces S of TiO and BiVO, in a molar ratio of 1: 4 or 4: 1

twenty four

Even in this case, it has been shown that a photocatalyst having the highest activity under visible light can be obtained.

[0009] In addition, the second aspect of the present invention is a general formula BiTiMO (wherein M is composed of V, Nb, and Ta).

6

A complex metal oxide represented by (2) represents a photocatalyst having high activity under visible light. In particular, BiTiVO for M force SV

6 can be a photocatalyst with significantly high activity under visible light.

Here, the general formula BiTiMO (wherein M is at least selected from the group consisting of V, Nb and Ta)

6

The composite metal oxides represented by (1) represent NH VO, Nb 2 O and Ta 0

4 3 2 5 2 5 A powder mixture of one selected from Bi O and TiO for a predetermined time at a predetermined temperature condition

2 3 2

Bake under (first baking process), then cool down and pulverize, and fire again at a higher temperature than the first baking process for a predetermined time (second baking process), and then cool gently It is produced by.

Here, it is preferable that the first firing step and the second firing step described above are performed under high humidity. Performing under high humidity means, for example, putting water in a reaction vessel.

Further, it is preferable that the first firing step described above is performed under a temperature condition of 550 to 750 ° C., and the second firing step is performed under a temperature condition of 800 to 900 ° C. Specific production conditions will be described in the following examples, but it is more preferable that the first baking step is performed at 700 ° C. for 30 hours and the second baking step is performed at 850 ° C. for 30 hours.

Further, it is more preferable that the composite metal oxide obtained by the above production method is further subjected to etching treatment in hydrochloric acid or sulfuric acid. The particle shape and size of the composite metal oxide change, the specific surface area per gram increases, and the activity improves.

Further, it is more preferable that the composite metal oxide obtained by the above production method is further pulverized by a ball mill. The specific surface area per unit gram increases and the activity improves.

[0010] Further, the third aspect of the present invention is that any one of CaO, NiO, and ZnO metal oxides is combined with a BiVO photocatalyst system, and the composition element is Bi, L (L = Ca, Ni, Zn). , V elements included

Four

The composite metal oxide can be a photocatalyst having high activity under visible light. [0011] The fourth aspect of the present invention is that the general formula BiL VO (wherein L is composed of Ca, Ni and Zn).

2 6

A composite metal oxide represented by at least one element selected from the group described above can be a photocatalyst having high activity under visible light.

Here, the general formula BiL VO (where L is selected from the group consisting of Ca, Ni and Zn forces)

2 6

The composite metal oxide represented by (2) represents a powder mixture of a metal oxide selected from CaO, NiO, and ZnO and BiO and TiO for a predetermined time under a predetermined temperature condition. so

2 3 2

Fired (first firing process), then cooled and pulverized, then fired again for a predetermined time under higher temperature conditions than the first firing process (second firing process), and then gently cooled to produce It is characterized by being.

A fifth aspect of the present invention is that the composite metal oxide shown in the first to fourth aspects of the present invention can be used as a photocatalyst by using it in the form of a fine particle thin film.

[0013] The sixth aspect of the present invention is that the composite metal oxide shown in the first to fourth aspects of the present invention can be used as a photocatalyst by using it in a suspension state.

[0014] Further, a seventh aspect of the present invention is to photolyze water under light irradiation including at least visible light using the photocatalyst according to any one of the first to sixth aspects of the present invention. It can be used as a method for producing oxygen and hydrogen.

[0015] Further, an eighth aspect of the present invention is the use of the photocatalyst according to any one of the first to sixth aspects of the present invention under the irradiation of light containing at least visible light (such as methanol). Photolysis It can be utilized as a purification method characterized by doing.

[0016] Further, the ninth aspect of the present invention is to provide a photocatalyst according to any one of the first to fourth aspects of the present invention by coating the surface of the substrate, thereby providing a wide variety of applications of the photocatalyst. It can be applied to the fields (antifouling self-cleaning 'antibacterial / anti-fogging field, air purification, water purification, etc.).

[0017] Further, a tenth aspect of the present invention provides a photocatalyst, a photosensor, and a photovoltaic cell using a visible light responsive coating material containing the photocatalyst according to any one of the first to fourth aspects of the present invention as a material. It can be used as a material, a photofouling material, a photohydrophilic material, a photobacterial material, and the like.

The invention's effect

[0018] Photocatalyst has already been commercialized and released, but so far only ultraviolet light using Ti〇 is used.

2

There are many things that cannot be used, and the practical activity is low. Since the novel composite metal oxide according to the present invention has a high sensitivity to visible light, the activity is greatly improved, and a small amount of photocatalyst can be achieved in conventional applications, and it has not been possible to use due to insufficient activity until now. Since the application can be expanded to the area, the application is greatly expanded.

In particular, the new BiTiVO particulate photocatalyst is visible to improve the utilization efficiency of sunlight.

6

It is a photocatalyst with high photoresponsiveness and has great practical potential.

In addition, since the photocatalyst of the present invention has both high oxidation ability and reduction ability with respect to other substances, for example, organic substance decomposition reaction, metal ion reduction reaction, or nitrogen It can also be applied to environmental purification such as oxide treatment, and has the effect of photolyzing endocrine disrupting substances present in the system to be purified, particularly the system to be purified. BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, a preferred embodiment of the photocatalyst of the present invention will be specifically described by taking as an example the case where it is applied to composition, production method, water decomposition or organic substance decomposition. The embodiments of the present invention are described for better understanding of the gist of the invention, and do not limit the contents of the invention unless otherwise specified.

[0020] The method for producing the photocatalyst according to the present invention is not particularly limited, and can be produced by a known method such as a solid phase method, a wet method, or a gas phase method. Method Is described below.

[0021] A novel photocatalyst BiTiVO fine particle thin film which is an embodiment of the present invention is produced by a solid phase method

6

In the method, temperature and time are important conditions.

First, oxides of the respective metal components as raw materials are mixed at a predetermined composition ratio, and, for example, fired in the atmosphere at a firing temperature of 700 ° C. for 30 hours. Next, it is cooled to room temperature, pulverized by force, and then fired again at a firing temperature of 850 ° C. for 30 hours. This makes it possible to produce the desired photocatalyst.

[0022] The resulting photocatalyst BiTiVO mixed metal oxide fine particles into a suspension or thin film form

6

When light is irradiated, excited electrons and holes are generated in the fine particles, which cause a reduction reaction and an oxidation reaction on the surface of the fine particles, respectively.

The photocatalyst BiTiVO according to the present invention has high oxidation ability and reduction ability with respect to other substances.

6

In addition, it can be applied not only to the decomposition reaction of water but also to environmental purification such as the decomposition reaction of organic substances, the reduction reaction of metal ions, or the treatment of nitrogen oxides.

FIG. 1 shows a diffuse reflectance spectrum of the photocatalyst BiTiVO which is an embodiment of the present invention.

6

In addition, as a reference, the wavelength dependence of solar energy density (Solar Spectrum) is plotted. In the Solar Spectrum shown in the figure, when the wavelength is 400 nm or less, ultraviolet light, 400 nm to 750 nm is visible light, and 750 awakening is infrared light region, the photocatalyst according to the present invention BiTiV O force diffuse reflection in the visible light region The spectrum is broad

6

I can understand. Titanium dioxide (Ti) that responds to ultraviolet rays but does not respond to visible light

O) In the case of a photocatalyst, no absorption is observed in the diffuse reflectance spectrum above 400 awakenings

2

In contrast, the photocatalyst BiTiVO according to the present invention absorbs from 400 nm to 800 nm.

6

Can be observed.

FIG. 2 shows a horizontal axis obtained from the diffuse reflection spectrum of the photocatalyst BiTiVO according to the present invention.

6

Is an absorption spectrum diagram in which the scale is changed from wavelength to light energy. Figure 2 shows that the photocatalyst BiTiVO according to the present invention has a narrow band gap of 2. leV.

6

It can be understood that it absorbs light in the visible light region.

[0025] Hereinafter, the present invention will be specifically described by way of examples. This is not something that can be interpreted. The apparatus used for observing the composition and morphology of the resulting photocatalyst will be described below.

The composition of the sample was identified using XPS (ESCA 2000, manufactured by Shimadzu Corporation). The crystal form is determined with XRD (manufactured by Philips, model: X'Pert Diffractometer), and the observation of granular morphology is performed with a scanning electron microscope (SEM) (manufactured by Hitachi, model: S-5000). The diffuse reflection spectrum was measured with an ultraviolet-visible near-red spectrophotometer (manufactured by JASCO, model: V-570). A combination of a filter that cuts off light with a wavelength of 420 nm or less (L42 cut-off filter) and a 300W Xe lamp was used as the light source for oxygen generation. The light source for decomposing organic matter was measured using a combination of a filter that cuts off light with a wavelength of 420 nm or less (L42 cut-off finolator) and a 300 W Xe lamp.

Example 1

[0026] (Photocatalyst BiTiVO, BiTiNbO, BiTiTaO Fine Particle Manufacturing Method)

6 6 6

First, a method for producing fine particles of the photocatalyst BiTiVO according to the present invention will be described. As reactant

6

Bi O (99.99%, Wako), TiO (ST-01), NH VO (99.0%, Wako)

2 3 2 4 3

Mix the appropriate amount in powder form. Next, the mixed reaction product is first calcined, for example, in the air at a calcining temperature of 700 ° C. for 30 hours. Then, after cooling to room temperature and finely pulverizing, the second baking is performed again at a baking temperature of 850 ° C. for 30 hours. And the target photocatalyst can be manufactured by slow cooling. The result is a dark yellow powder (powder).

Similarly, the photocatalyst BiTiNbO according to the present invention

6. Fine particles of BiTiTaO are the above-mentioned photocatalyst

6

In the production method of BiTiVO fine particles, Nb O and Ta

6 4 3 2 5 2 5 is first fired at a firing temperature of 850 ° C for 30 hours. And after cooling to room temperature and finely pulverizing, it is baked again at 1000 ° C for 12 hours.

In addition, overproduction of the photocatalysts BiTiVO, BiTiNbO, and BiTiTaO produced by the above method.

In about 6 6 6, for example, by carrying out sintering reaction under high humidity conditions such as putting water in the reaction vessel.

Furthermore, it becomes possible to improve the activity of the photocatalyst.

[0027] Fig. 3 shows a diffuse reflection spectrum of the photocatalyst BiTiVO, BiTiNbO, BiTiTaO according to the present invention.

6 6 6

Torr. FIG. 4 shows the photocatalysts BiTiVO, BiTiNbO, and BiTiTaO according to the present invention. An absorption spectrum diagram with the horizontal axis scaled from wavelength to optical energy, obtained from the diffuse reflectance spectrum, is shown.

In addition, in Table 1 below, the photocatalyst BiTiVO, BiTiNbO, BiTiTaO fine particle production method

6 6 6

Fig. 3 and Fig. 4 show the band gap obtained (color) and the color of the photocatalyst powder that is the product of the reaction (Original materials).

[table 1]

[0029] Fig. 5 shows a known visible light responsive photocatalyst, bismuth vanadate (BiVO) and two

4 Diffuse reflection spectrum of photocatalyst BiTiVO according to the present invention in comparison with titanium oxide

6

Show. Figure 5 shows that bismuth vanadate (BiVO) is a known visible light responsive photocatalyst.

4 absorbs light with a wavelength up to 550 mm, whereas the photocatalyst BiT iVO according to the present invention can absorb light with a wavelength up to 700 nm and has excellent visible light response.

6

I understand that. Currently, the photocatalyst TiO, which is in practical use,

2

The photocatalyst BiTiVO according to the present invention absorbs ultraviolet light of a wavelength,

6

This indicates that there is a possibility of a photocatalyst that can absorb the visible light region and can efficiently convert solar energy compared to the medium.

[0030] FIG. 6 is a schematic view of a photocatalytic BiTiVO powder according to the present invention, which is obtained from NalO aqueous solution by irradiation with visible light.

6 3

The oxygen generation characteristics of the present invention are shown in comparison with the known photocatalysts BiVO and WO.

4 3

The oxygen generation reaction using various photocatalysts in Fig. 6 was carried out in a closed circulation system. Catalysts include BiTiVO (1-2 μ ΐη) powder, BiVO (0.1-0.2 μ パウダー η) powder, and commercially available W ○ (

6 4 3

0.2 to 0.3 μΐη) powder was used. 50 mg of catalyst in NalO aqueous solution (0.01 mol / L, 50 mL) Into a suspension and irradiated with visible light (> 420 nm). Buffering agent for pH adjustment La ○

twenty three

(50 mg) was used. A 300W Xe lamp equipped with a filter (L42) that cuts off light with a wavelength of 420 nm or less was used as the light source. The produced oxygen was quantified using gas chromatography (Shimadzu, GC-148).

From FIG. 6, the photocatalyst BiTiVO powder according to the present invention is compared with the known photocatalysts BiVO and WO.

4 3 6 The slope of the graph is steeper at the end. In other words, it can be understood that the oxygen generation activity of this photocatalyst is high because the amount of oxygen gas generated per unit time (reaction rate) is large.

Example 2

[0031] (decomposition of water)

As described above, it has been suggested that the photocatalyst of the present invention can be used as a method for producing oxygen and / or hydrogen by photodegrading water under light irradiation including at least visible light. This will be described below while showing.

FIG. 7 is a graph of photocurrent quantum yield (IPCE) of the photocatalytic BiTiVO fine particle thin film according to the present invention.

6

Show the spectrum spectrum.

Here, the measurement conditions were a BiTiVO thin film electrode in a solution of electrolyte Na SO (0.5 M).

A potential (0.4V, 0.5V, 1.0V, 1.2V, 1.3V) is applied to the 2 4 6 electrodes with reference to the Ag / AgCl reference electrode. Figure 7 shows the wavelength dependence of the photocurrent quantum yield of the BiTiVO thin film electrode.

6

It can be understood that the photocurrent due to the oxidative decomposition of water starts at a wavelength of 500 nm, and that the oxidative decomposition of water occurs for visible light irradiation up to around 500 nm.

[0032] FIG. 8 shows the photocatalytic BiTiVO fine particle thin film and the photocatalytic BiVO fine particle thin film according to the present invention.

6 4 The action spectrum of photocurrent quantum yield (IPCE) in the form of contrast with the membrane electrode (in the case of potential 1.0V) is shown. Figure 8 shows that the present photocatalyst compared to the BiVO fine particle thin film electrode.

Four

Photocatalytic BiTiVO fine particle thin film is more effective for visible light irradiation up to around 500mm

6

Thus, it can be understood that the water has an extremely high photoactivity in the oxidative decomposition reaction of water. This is a representation of the results of Figure 6 from another aspect, confirming the results of Figure 6.

FIG. 9 shows a surface SEM photograph of the photocatalytic BiTiVO fine particles according to the present invention. this

6

From the SEM photograph, BiTiVO powder is a fine particle with high crystallinity and an average particle size of 1-2 / η

6

It turns out that it is. Typical photocatalyst already known TiO particle size is 20-40nm, and BiV

2

While the particle size of O is 100 to 200 nm, the photocatalyst BiTiVO particles of the present invention

4 6 The child size is as large as 1000-2000nm. Since the activity of the photocatalyst is proportional to the surface area of the particles, it is expected that the activity of the photocatalyst BiTiVO of the present invention will be further improved by further reducing the particle size.

6

FIG. 10 shows the photocatalytic BiTiVO fine particles (Bi4f, Ti2p, V2p, ○ ls of the present invention).

6

Shows XPS spectrum (in the area). It can be seen from this that the metal ions in the fine particles exist with the valences of Bi ³⁺ , Ti ⁴⁺ , and V ⁵⁺ , and have the surface composition of BiTiVO from their respective peak areas and sensitivity factors.

6

FIG. 11 shows a photocurrent one-potential curve of the photocatalytic BiTiVO fine particle thin film electrode according to the present invention.

6

Show. In addition, Fig. 12 shows the photocurrent-potential curve of the photocatalytic BiVO fine film electrode for comparison

Four

Show the line. Reducing agent (I-, Me〇H, SCN-, Br-, respectively) in electrolyte solution (0.5M Na 2 SO 4)

twenty four

) Was added, and the photocurrent was measured under simulated sunlight ((AM1.5G, lOOmW m ² ) irradiation).

As understood from FIGS. 11 and 12, the photocatalytic BiTiVO fine particle thin film electrode according to the present invention

6

Compared to the existing BiVO, all reducing agents are exposed to photoelectric under pseudo-sunlight irradiation.

Four

The current is about 10 times larger and the oxidation photocurrent starts to flow from a more negative potential. From now on, the photocatalyst BiTiVO fine particle thin film electrode according to the present invention is more in solution than the existing BiVO.

6 4

It was confirmed that it has a significantly higher activity against the photo-oxidative degradation of various substances present.

Example 3

[0035] (Decomposition of organic matter)

As described above, the photocatalyst of the present invention has both high oxidation ability and reduction ability with respect to other substances. Therefore, for example, the decomposition reaction of organic substances and the reduction of metal ions are not limited to the decomposition reaction of water. It can also be applied to environmental purification such as reaction or treatment of nitrogen oxides, and it can photolyse endocrine disrupting substances present in the system to be purified, especially the system to be purified.

Hereinafter, the methanol decomposition reaction as an organic substance decomposition reaction will be described with specific data. Figure 13 shows the photoelectric flow rate of the photocatalytic BiTiVO fine particle thin film according to the present invention. The action spectrum in the presence of methanol of the child yield (IPCE) is shown in comparison with the absence of methanol. By adding methanol, a significant increase in photooxidation current was confirmed for visible light irradiation up to about 500 nm. This is because BiTiVO fine particles are water acid

6

It shows high activity under visible light irradiation not only for oxidization but also for photo-oxidative degradation of organic substances such as methanol.

Example 4

[0036] (Photolysis of water and methanol with BiZn VO)

2 6

So far, we have shown examples of BiTiVO photocatalysts.

6 4 Photocatalyst according to the present invention prepared by combining BiZn VO with water and methanol

2 6

An example of decomposition is shown. Here, BiZn VO is a reaction product of Bi O (99.99%, Wako), Zn

2 6 2 3

0 (99.9%, manufactured by Wako), NH VO (99.0%, manufactured by Wako), for example, in the atmosphere, firing temperature

4 3

First firing at 700 ° C for 30 hours. Then, after cooling to room temperature and finely pulverizing, the second baking is performed again at a baking temperature of 850 ° C. for 30 hours. And the target photocatalyst can be manufactured by slow cooling. The diffuse reflectance spectrum of this powder is shown in FIG. BiZn VO according to the present invention has strong absorption in the visible light region up to about 530 nm.

2 6

Karu. Figure 15 shows the photocatalytic BiZn VO fine particle thin film electrolyte Na SO (0.5

2 6 2 4

The action spectrum of the photocurrent quantum yield (IPCE) in the solution of M) is shown. Even when methanol was not present in the solution (in the case of no reductant), a photocurrent was observed in the visible light region up to about 530 nm. This indicates that this photocatalyst has the ability to generate oxygen by photo-oxidative decomposition of water under visible light irradiation. Furthermore, by the presence of methanol in the solution, a significant increase in photooxidation current was confirmed for visible light irradiation up to about 530 mm. This is because BiZn VO fine particles are not only oxidized by photooxidation of water but also methanol.

2 6

It shows high activity under visible light irradiation even for photo-oxidative degradation of organic substances such as alcohol.

Example 5

[0037] In this Example 5, the photocatalyst BiZn VO prepared in Example 4 is taken as an example, and the activity is further increased.

2 6

A method of improving will be described. Photocatalyst BiZn VO is used as a reactant as described above.

2 6

Bi〇 (99.99%, Wako), Zn〇 (99.9%, Wako), NH VO (99.0%, Wako) are used. A suitable amount of these powders are mixed and fired at a firing temperature of 800 ° C for 30 hours in the air. The resulting powder is etched in H 2 SO (0.5 M). And live

twenty four

The property can be further improved.

Figure 16 shows the oxygen generation characteristics of the photocatalytic BiZn VO powder by visible light irradiation. FIG. 16

2 6

In the graph, a is a photocatalyst without etching in H 2 SO (0.5 M) BiZ

twenty four

n shows VO powder, b shows etching time in H 2 SO 4 (0.5 M) for 24 hours

2 6 2 4

The photocatalyst performed is for BiZn VO powder, c is the etch in H 2 SO (0.5 M).

2 6 2 4

The photocatalytic BiZn VO powder was processed for 48 hours.

2 6

More specifically, the etching process is performed by placing BiZn VO powder l.Og in 50 ml of H 2 SO 4 (0.5 M).

2 6 2 4

The test was conducted at 70 ° C for 24 hours or 48 hours. After that, the BiZn VO powder that had been cleaned and etched was annealed at 300 ° C.

2 6

Figure 16 shows that the oxygen generation characteristics are improved by about 2.7 times in the case where the etching process is performed for 24 hours (b) compared with the case where the etching process is not performed (a), and the etching process is performed for 48 hours. (B) shows that the oxygen evolution characteristics are improved by about 3.5 times.

Figure 17 shows an SEM photograph of the photocatalytic BiZn VO powder. Etched

2 6

When comparing the non-etched material ((a) in Fig. 17) with the sample that had been etched for 24 hours ((b) in Fig. 17), it was found that the surface roughness of the etched powder increased. Recognize. Thus, the etching process changes the powder particle shape and size, increases the specific surface area per unit gram, and improves the activity.

Etching is not limited to the photocatalytic BiZn VO powder, but the photocatalyst BiTi described above.

2 6

It is also useful for VO. In the case of photocatalyst BiTiVO, it is preferable to use hydrochloric acid.

6 6

Good.

Example 6

In this example, two photocatalytic systems of TiO and BiVO were blended at a molar ratio of 1: 4 and 1: 2.

twenty four

In this case, the molar ratio of the mixture is 4: 1 and 2: 1, and the diffuse reflection spectrum and the photocurrent potential curve of the thin film electrode are shown. From these, two photocatalytic systems of TiO and BiVO

twenty four

It can be understood that it functions as a photocatalyst with high activity even when the mixing ratio of is freely changed. Industrial applicability

[0039] The photocatalyst according to the present invention is excellent in visible light responsiveness, for purifying air and water, antifouling walls and glass, sterilizing hospital walls, and generating hydrogen by sunlight. Available. In other words, it can be used for outdoor antifouling purposes using sunlight (for example, coating, exterior materials such as building materials, sound insulation materials, vehicle side mirrors, etc.). In addition, it uses visible light such as sunlight and fluorescent lamps for purposes such as antifouling, deodorizing, and antibacterial purposes indoors and cars (interior materials such as paint, porcelain, glass, and building materials, furniture, home appliances, It can be used for electric lights).

Brief Description of Drawings

FIG. 1 shows a diffuse reflection spectrum of the photocatalyst BiTiVO according to the present invention.

6

[Fig. 2] Waves on the horizontal axis obtained from the diffuse reflection spectrum of the photocatalyst BiTiVO according to the present invention.

6

The absorption spectrum figure which changed the scale from light to light energy is shown.

[Fig. 3] Diffuse reflection spectra of photocatalysts BiTiVO, BiTiNbO and BiTiTaO according to the present invention

6 6 6

Indicates.

[Fig. 4] Diffuse reflection spectra of photocatalysts BiTiVO, BiTiNbO and BiTiTaO according to the present invention

6 6 6

Fig. 2 shows an absorption spectrum obtained by changing the scale from wavelength to light energy on the horizontal axis, as determined by force.

[Fig.5] Comparison of photocatalyst BiTiVO according to the present invention in comparison with photocatalyst BiVO and TiO

4 2 6 Shows the diffuse reflectance spectrum.

FIG. 6: Photocatalytic BiTiVO powder according to the present invention in comparison with photocatalyst BiVO and WO

4 3 6 Oxygen generation characteristics from NalO aqueous solution by visible light irradiation at the end are shown.

Three

[Fig.7] Photocurrent Quantum of Photocatalyst BiTiVO Fine Particle Film According to the Present Invention at Various Potentials

6

[Fig. 8] Photocatalytic BiTiVO fine particle thin film and photocatalytic BiVO fine particle thin film electrode according to the present invention

6 4

2 shows the action spectrum of photocurrent quantum yield (IPCE) in the form of contrast of (when the potential is 1.0 V).

FIG. 9 shows a surface SEM photograph of the photocatalytic BiTiVO fine particles according to the present invention.

6

[Fig. 10] XPS spectra of photocatalytic BiTiVO fine particles according to the present invention (Bi4f, Ti2p, V2p,

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O Is area). 11] A photocurrent-potential curve of the photocatalytic BiTiVO fine particle electrode according to the present invention is shown.

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[Figure 12] Photocatalytic potential curve of photocatalyst BiVO fine particle electrode under simulated sunlight irradiation

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Indicates.

13] Photocatalyst according to the present invention Photoelectric flow rate in the presence of methanol of BiTiVO fine particle thin film

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This shows the action ratio of the yield (IPCE) (when the potential is 1.0 V).

14] A diffuse reflection spectrum of the photocatalyst BiZn VO according to the present invention is shown.

2 6

FIG. 15 is a graph of photocurrent quantum yield (IPCE) of the photocatalytic BiZn VO fine particle film according to the present invention.

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The spectrum is shown with and without methanol (when the potential is 1.0 V with reference to the Ag / AgCl reference electrode).

FIG. 16 shows the characteristics of oxygen generation by visible light irradiation of photocatalyst BiZn VO powder.

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FIG. 17 shows an SEM photograph of the photocatalytic BiZn VO powder.

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[Figure 18] Photocatalyst BiTiVO XRD pattern (FT 〇 top)

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[Figure 19] When two photocatalytic systems of TiO and BiVO are mixed at a molar ratio of 1: 4 and 1: 2.

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The combined diffuse reflectance spectrum is shown.

[Figure 20] Thin film when two photocatalytic systems of TiO and BiVO are mixed at a molar ratio of 1: 2.

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The photocurrent potential curve of an electrode is shown.

[Fig.21] When two photocatalytic systems of TiO and BiVO are mixed at a molar ratio of 4: 1 and 2: 1

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The combined diffuse reflectance spectrum is shown.

[Figure 22] Thin film when two photocatalytic systems of TiO and BiVO are mixed at a molar ratio of 2: 1

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The photocurrent potential curve of an electrode is shown.

Claims

The scope of the claims

[I] Combining two photocatalytic systems of TiO and BiVO, and using Bi, Ti, and V elements as composition elements

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A photocatalyst comprising a mixed metal oxide.

[2] Two photocatalytic systems of TiO and BiVO are blended in a molar ratio of 1: 9 to 9: 1.

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A photocatalyst characterized by being a complex metal oxide containing Bi, Ti, and V elements as constituent elements

[3] General formula BiTiMO (wherein M is at least one selected from the group consisting of V, Nb and Ta)

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A complex metal oxide represented by:

[4] Powder mixture of one selected from NH VO, Nb 2 O and Ta 2 O and Bi 2 O and TiO

4 3 2 5 2 5 2 3 2 The compound is calcined for a predetermined time under a predetermined temperature condition (first calcining process), then cooled and pulverized after a while, and again at a higher temperature than the first calcining process for a predetermined time. Composite metal oxide produced by firing under conditions (second firing step) and then cooling gently

[5] The composite metal oxide according to claim 4, wherein the first firing step and the second firing step are performed under high humidity.

[6] The first firing step is performed under a temperature condition of 550 to 750 ° C, and the second firing step is performed under a temperature condition of 800 to 900 ° C. Or a composite metal oxide as described in 5.

[7] A composite metal oxide, wherein the composite metal oxide according to any one of claims 3 to 6 is further etched in hydrochloric acid or sulfuric acid.

[8] A composite metal oxide, wherein the composite metal oxide according to any one of claims 3 to 6 is further pulverized by a ball mill.

[9] The composite metal oxide according to any one of [3] to [8], which has a function as a photocatalyst.

[10] Combining one of the CaO, NiO, and ZnO metal oxides with the BiVO photocatalyst system,

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A photocatalyst characterized by being a composite metal oxide containing Bi, L (L = Ca, Ni, Zn), and V elements as composition elements.

[II] General formula BiL VO (wherein L is at least one selected from the group consisting of Ca, Ni and Zn) A complex metal oxide represented by:

[12] A powder mixture of a metal oxide selected from CaO, NiO, and ZnO and BiO and TiO.

2 3 2

Baked for a predetermined time at a predetermined temperature condition (first baking step), and then cooled down and powdered again, and again baked at a higher temperature than the first baking step for a predetermined time (second baking step), A composite metal oxide produced by subsequently cooling gently.

[13] The composite metal oxide according to claim 12, wherein the first firing step and the second firing step are performed under high humidity.

[14] The first firing step is performed under a temperature condition of 550 to 750 ° C, and the second firing step is performed under a temperature condition of 800 to 900 ° C. Or the composite metal oxide according to 13.

[15] A composite metal oxide, wherein the composite metal oxide according to any one of claims 11 to 14 is etched in hydrochloric acid or sulfuric acid.

16. The composite metal oxide according to any one of claims 11 to 15, which has a function as a photocatalyst.

[17] The mixed metal oxide according to any one of claims 3 to 6, or the claims 11 to 1.

5. A photocatalyst, wherein the composite metal oxide according to item 1 is formed into a fine particle thin film.

[18] The mixed metal oxide according to any one of claims 3 to 6 or the mixed metal oxide according to any one of claims 11 to 15 is used in the form of a suspension. A photocatalyst characterized by

[19] The power of any one of claims 1, 2, 10, 17, and 18, wherein the photocatalyst according to claim 1 is used to photolyze water under light irradiation including at least visible light, and oxygen and Z or hydrogen production method.

[20] The photocatalyst according to any one of claims 1, 2, 10, 17 and 18, wherein the photocatalyst according to item 4 is used to photolyze organic matter (such as methanol) under light irradiation including at least visible light. Purification method.

[21] An article comprising the photocatalyst according to any one of claims 1, 2, 10, 17, and 18 coated on the surface of the substrate. A visible light responsive paint comprising the photocatalyst according to any one of claims 1, 2, 10, 17, and 18 as a material.